1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device having a mixer built in.
2. Description of the Related Art
In wireless communication, an image rejection mixer is frequently used in order to effect a reduction in cost. This image rejection mixer does not require a built-on image rejection filter but instead uses two mixer circuits MX1 and MX2 as shown in FIG. 7, which results in an increase in power dissipation.
The operation of the conventional image rejection mixer will be described with reference to FIGS. 7 and 8. In the description which follows, it is assumed that ωi>ωL0>ωd and ωIF=ωL0−ωd. A radio-frequency received signal (hereinafter referred to as an RF signal) containing an image signal is represented by cos ωdt+cos ωit, and a local signal (hereinafter referred to as an LO signal), which is a conversion carrier signal, is represented by cos ωL0 (amplitudes are omitted for simplicity).
First, an RF signal is input to each of the first and second mixer circuits MIX1 and MIX2, which are supplied with LO signals between which a phase difference of 90 degrees has been introduced through a first phase shifter 11. Consider here that the LO signal input to the first mixer circuit MIx1 has its phase shifted by 90 degrees and the phase of the LO signal to the second mixer circuit MIX 2 remains unchanged.
The RF signal and the LO signal are mixed in each of the mixer circuits MIx1 and MIX2. As a result, intermediate-frequency signals (hereinafter referred to as IF signals) x1(t) and x2(t) are output from the mixer circuits MIx1 and MIX2, respectively. These IF signals have their high-frequency components removed through lowpass filters and are represented by                                                                         x1                ⁡                                  (                  t                  )                                            =                            ⁢                                                (                                                            cos                      ⁢                                                                                           ⁢                      ω                      ⁢                                                                                           ⁢                      dt                                        +                                          cos                      ⁢                                                                                           ⁢                      ω                      ⁢                                                                                           ⁢                      it                                                        )                                ×                                  {                                      cos                    (                                                                  ω                        ⁢                                                                                                   ⁢                        LOt                                            -                                              π                        /                        2                                                              )                                    }                                                                                                        =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    +                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                          sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                                                                                                                        ⁢                                                sin                  ⁢                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        i                                            +                                              ω                        ⁢                                                                                                   ⁢                        LO                                                              )                                                  +                                  sin                  ⁡                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        i                                            -                                              ω                        ⁢                                                                                                   ⁢                        LO                                                              )                                                              }                                                                          =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    +                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                          sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                                                                                                                        ⁢                                                sin                  ⁢                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        i                                            +                                              ω                        ⁢                                                                                                   ⁢                        LO                                                              )                                                  -                                  sin                  ⁡                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        LO                                            -                                              ω                        ⁢                                                                                                   ⁢                        i                                                              )                                                              }                                                                          =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            L                            ⁢                                                                                                                   ⁢                            O                                                                          )                                                              -                                          sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            LO                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            i                                                                          )                                                                              }                                                                                        (        1        )                                                                                    x2                ⁡                                  (                  t                  )                                            =                            ⁢                                                (                                                            cos                      ⁢                                                                                           ⁢                      ω                      ⁢                                                                                           ⁢                      dt                                        +                                          cos                      ⁢                                                                                           ⁢                      ω                      ⁢                                                                                           ⁢                      it                                                        )                                ×                cos                ⁢                                                                   ⁢                ω                ⁢                                                                   ⁢                LOt                                                                                        =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            cos                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    +                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                          cos                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                                                                                                                        ⁢                                                cos                  ⁢                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        i                                            +                                              ω                        ⁢                                                                                                   ⁢                        LO                                                              )                                                  +                                  cos                  ⁡                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        i                                            -                                              ω                        ⁢                                                                                                   ⁢                        LO                                                              )                                                              }                                                                          =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            cos                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    +                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                          cos                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                                                                                                                        ⁢                                                cos                  ⁢                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        i                                            +                                              ω                        ⁢                                                                                                   ⁢                        LO                                                              )                                                  +                                  cos                  ⁡                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        LO                                            -                                              ω                        ⁢                                                                                                   ⁢                        i                                                              )                                                              }                                                                          =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            cos                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                          cos                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            LO                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            i                                                                          )                                                                              }                                                                                        (        2        )            
Next, a phase shift of 90 degrees is introduced between the IF signals x1(t) and x2(t) in the second phase shifter 12. It is assumed here that the phase of the IF signal x2(t) is shifted by 90 degrees and the phase of the IF signal x1(t) is not shifted. Therefore, the IF signal x1(t) is output as it is onto a signal path 1 and an IF signal ×3(t) is output onto a signal path 2, which is represented by                                                                         x3                ⁡                                  (                  t                  )                                            =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            cos                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                    -                                                      π                            /                            2                                                                          )                                                              +                                          cos                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            L                            ⁢                                                                                                                   ⁢                            O                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            i                                                    -                                                      π                            /                            2                                                                          )                                                                              }                                                                                                        =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              +                                          sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            LO                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            i                                                                          )                                                                              }                                                                                        (        3        )            
The IF signals x1(t) and ×3(t) are next added together in an adder 13 to produce a signal IFOUT1, which is represented by                                                         IFOUT1              =                            ⁢                                                x1                  ⁡                                      (                    t                    )                                                  +                                  x3                  ⁡                                      (                    t                    )                                                                                                                          =                            ⁢                                                (                                      1                    /                    2                                    )                                ⁢                                  {                                                            sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            d                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            LO                                                                          )                                                              -                                          sin                      ⁡                                              (                                                                              ω                            ⁢                                                                                                                   ⁢                            LO                                                    -                                                      ω                            ⁢                                                                                                                   ⁢                            i                                                                          )                                                              +                                                                                                                                        ⁢                                                sin                  ⁢                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        d                                            -                                              ω                        ⁢                                                                                                   ⁢                        LO                                                              )                                                  +                                  sin                  ⁡                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        LO                                            -                                              ω                        ⁢                                                                                                   ⁢                        i                                                              )                                                              }                                                                          =                            ⁢                              sin                ⁡                                  (                                                            ω                      ⁢                                                                                           ⁢                      d                                        -                                          ω                      ⁢                                                                                           ⁢                      LO                                                        )                                                                                                        =                            ⁢                              -                                  sin                  ⁡                                      (                                                                  ω                        ⁢                                                                                                   ⁢                        LO                                            -                                              ω                        ⁢                                                                                                   ⁢                        d                                                              )                                                                                                          (        4        )            
As indicated by expression (4), a desired component ωd only is left in ωIF (=ωL0−ωd). That is, adding x1(t) and ×3(t) together allows the image signal to be rejected without using an external filter.
In comparison with the external image rejection filter, however, the conventional image rejection mixer has a problem of large power dissipation because of the provision of two mixer circuits.